Trichalcogenasupersumanenes and its concave-convex supramolecular assembly with fullerenes

Synthesis of buckybowls have stayed highly challenging due to the large structural strain caused by curved π surface. In this paper, we report the synthesis and properties of two trichalcogenasupersumanenes which three chalcogen (sulfur or selenium) atoms and three methylene groups bridge at the bay regions of hexa-peri-hexabenzocoronene. These trichalcogenasupersumanenes are synthesized quickly in three steps using an Aldol cyclotrimerization, a Scholl oxidative cyclization, and a Stille type reaction. X-ray crystallography analysis reveals that they encompass bowl diameters of 11.06 Å and 11.35 Å and bowl depths of 2.29 Å and 2.16 Å for the trithiasupersumanene and triselenosupersumanene, respectively. Furthermore, trithiasupersumanene derivative with methyl chains can form host-guest complexes with C60 or C70, which are driven by concave-convex π ⋯ π interactions and multiple C–H ⋯ π interactions between bowl and fullerenes.

All reagents and starting materials were obtained from commercial suppliers and used without further purification unless otherwise noted. All air or moisture sensitive reactions were carried out under an argon atmosphere by standard Schlenk techniques. Anhydrous toluene and Et2O were distilled from sodium-benzophenone immediately prior to use. Anhydrous dichloromethane (DCM) was distilled from CaH2. The reactions were monitored using analytical thin layer chromatography (TLC, GF-254). Tributyltinselenide, (Bu3Sn)2Se, was prepared according to literature procedure in 50 mmol scale. [1] Flash chromatography was performed using silica gel (200-300 mesh) with freshly distilled solvents.
The 1 H NMR and 13 C NMR spectra were recorded on a JEOL 400 MHz or a Bruker Avance 600 MHz spectrophotometer using CDCl3, Toluene-d8, or 1,2-dichlorobenzene-d4 as a solvent. Chemical shifts (δ) are reported in parts per million (ppm) using TMS as an internal standard. The terms m, s, d, t and q represent multiplet, singlet, doublet, triplet and quartet, respectively. The term (br.) is used when the peak is broad, and the correct multiplicity cannot be surely assigned. Coupling constants (J) are given in Hertz (Hz). The high-resolution mass spectra were recorded on a Bruker Avance spectrometer (maXis) (Operation Mode: APCI Positive Ion Mode, Analyzer Type: TOF). The crystal structure was recorded on Bruker D8 Venture X-ray single crystal diffraction spectrometer. Microwave reactions were performed with Xianghu XH-100A Microwave Irradiation Equipment.
UV-vis absorption spectra were recorded on a Hitachi U-3900/3900H spectrophotometer. Fluorescence spectra were performed on a fluorolog-3 fluorescence spectrophotometer (Horiba JY, USA). The fluorescence lifetime was measured using a FLSP920 fluorescence spectrophotometer. Absolute fluorescence quantum yields were measured on a HAMAMATSU Absolute PL Quantum Yield Measurement System C9920-02G at room temperature. Thermogravimetric analysis (TGA) measurements were performed on a STA 409 PC instrument under a dry nitrogen flow, heating from room temperature to 800 ºC, at a heating rate of 10 ºC/min. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed on a CHI 660B electrochemical analyzer at room temperature in inert atmosphere with a three-electrode configuration in CH2Cl2 solution (purchased from Sigma-Aldrich) containing the substrate (typically 2 × 10 -3 M) and 0.1 M tetrabutylammonium hexafluorophosphate (n-Bu4NPF6) as the supporting electrolyte. A platinum disc, a platinum plate, and a silver wire electrode were served as the working electrode, the counter electrode and the quasi-reference electrode (QRE), respectively. All potentials were calibrated versus an aqueous SCE by the addition of ferrocene as an internal standard taking E1/2(Fc/Fc + ) = 0.424 V vs. SCE. [2] The scan rate was 0.1 V/s. The HOMO and LUMO energy values were estimated from the onset potentials of the first oxidation and reduction event, respectively. The HOMO and LUMO energy levels were calculated according to the following equations: Where E1/2(Fc/Fc + ) is the half-wave potential of the Fc/Fc + couple against the SCE electrode. Theoretical calculations were carried out using the Gaussian 09, Revision D.01program. [3] 1.2 Synthetic procedures and characterization data [4] A mixture of chloroacetyl chloride (6.78 g, 60 mmol), AlCl3 (9.33 g, 70 mmol), and dichloromethane (100 mL) was cooled to -5 °C. A solution of 2,7-dichloro-9H-fluorene (11.76 g, 50 mmol) dissolved in dichloromethane (50 mL) was added. After 3-10 h, the deep-red reaction mixture was transferred to 15% aqueous hydrochloric acid (200 mL). After phase separation, the organic phase was washed twice with water. Dichloromethane was distilled off, while ethanol was added at the same rate. The crystallized product was isolated by filtration to give pure 2-chloro-1-(2,7-dichloro-9H-fluoren-4-yl)ethan-1-one (14.35 g, 92%); M.p.: 121-122 °C.

Synthesis of trifluorenocoronene (TFC, 4):
To a mixture of 3 (220 mg, 0.2 mmol, 1.0 equiv.) and DDQ (360 mg, 1.6 mmol, 8.0 equiv.) in 1,2dichloroethane (20 mL) was added trifluoromethanesulfonic acid (1 mL) under argon atmosphere, and the mixture was stirred at 50 °C for 6 h. After cooling to room temperature, the reaction mixture was quenched by adding saturated aqueous NaHCO3 (20 mL), and then the mixture was extracted with CH2Cl2 (3  30ml). The combined organic layer was dried over Na2SO4, and the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: petroleum ether) to give the trifluorenocoronene 4 (80 mg, 37%) as a yellow powder. M.p.: >300 °C.

Synthesis of trithiasupersumanene (1a):
In a glovebox, to an oven-dried pressure vessel with a Teflon screw cap was added compound 4 (110 mg, 0.1 mmol, 1.0 equiv.), Bu3SnSSnBu3 (245 mg, 0.4 mmol, 4.0 equiv.) and Pd(PPh3)4 (115 mg, 0.1 mmol, 1.0 equiv.) and 5 mL dry and degassed toluene. After the vessel was resealed and moved out from the glovebox, the mixture was heated and stirred at 150 °C for 48 h. On cooling to room temperature, the reaction mixture was quenched with saturated aqueous KF solution (30 mL) and extracted with CH2Cl2 (3  20ml). The combined organic phase was dried over anhydrous Na2SO4 before being filtered and concentrated down to a solid under reduced pressure. The crude solid was adsorbed onto silica gel and subjected to silica gel column chromatography (eluent: petroleum ether) to give the trithiasupersumanene 1a (57 mg, 58% yield) as a yellowish powder. M.p.: >300 °C.

Synthesis of triselenosupersumanene (1b):
In a glovebox, to an oven-dried pressure vessel with a Teflon screw cap was added compound 4 (110 mg, 0.1 mmol, 1.0 equiv.), Bu3SnSeSnBu3 [1] (263 mg, 0.4 mmol, 4.0 equiv.) and Pd(PPh3)4 (115 mg, 0.1 mmol, 1.0 equiv.) and 5 mL dry and degassed toluene. After the vessel was resealed and moved out from the glovebox, the mixture was heated and stirred at 150 °C for 48 h. On cooling to room temperature, the reaction mixture was quenched with saturated aqueous KF solution (30 mL) and extracted with CH2Cl2 (3  20ml). The combined organic phase was dried over anhydrous Na2SO4 before being filtered and concentrated down to a solid under reduced pressure. The crude solid was adsorbed onto silica gel and subjected to silica gel column chromatography (eluent: petroleum ether) to give the triselenosupersumanene 1b (44 mg, 39% yield) as a yellowish powder. M.p.: >300 °C.

Crystallographic details
High quality single crystals of compound 1a and 1b were grown by diffusing methanol into their solution in chloroform. After two weeks, orange crystals suitable for X-ray structural determination were obtained. The X-ray diffraction data were collected on Bruker D8 Venture X-ray single crystal diffractometer using Cu radiation at 153 K. Absorption correction was carried out by a multi-scan method. The structure was solved by direct methods with SHELXT [5] program and refined by least-square methods with SHELXL [6] program contained in Olex2 suite [7] . Details of the crystal and refinement results were listed in Supplementary Table 1 and Table 2.

X-ray Crystallography for (1a)
Supplementary  Average POAV angles for (1a) Supplementary Figure 9. POAV angles of 1a determined from the X-ray structure. The mean values were calculated by averaging the all values of equivalent position. POAV angles were calculated based on the three sigma bond angles at a conjugated carbon atom. [8] Butyl groups were omitted for clarity.

X-ray Crystallography for (1b)
Supplementary  POAV angles were calculated based on the three sigma bond angles at a conjugated carbon atom. [8] Butyl groups were omitted for clarity.

Average bond lengths and average BLA values for p-HBC
Supplementary Figure 19. Left: average bond lengths in Angstrom (Å) based on the result of X-ray crystal structure analysis; right: average bond length alternation (BLA) of rings based on the result of Xray crystal structure analysis. [9] The mean values were calculated by averaging the all values of equivalent position. The pronounced aromatic character with tiny BLA values of rings a and c were denoted as blue color.
Supplementary Figure 20. The comparison of average bond lengths (Å) in 1a, 1b and p-HBC based on the result of X-ray crystal structure analysis.

Photophysical Properties
UV-Vis absorption spectra were measured on a Hitachi U-3900/3900H spectrophotometer with dilute dichloromethane solution (1.0 × 10 -5 M) in spectral grade solvent at room temperature with a 1 cm square quarts cell. Emission spectra were measured on a fluorolog-3 fluorescence spectrophotometer (Horiba JY, USA) spectrophotometer with dilute solutions (1.0 × 10 -6 M) in spectral grade solvent in a 1 cm square quartz cell upon the excitation at 400 nm for both 1a and 1b. Absolute fluorescence quantum yields were determined on a HAMAMATSU Absolute PL Quantum Yield Measurement System C9920-02G calibrated integrating sphere system with diluted and deaerated solutions (10 −6 M order) in degassed spectral grade solvent at room temperature. The lifetimes of 1a were measured at room temperature with a FLSP920 fluorescence spectrophotometer with diluted and deaerated chloroform solutions (10 -6 M order). The results are summarized in Supplementary Table 3.

Electrochemical Properties
Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed on a CHI 660B electrochemical analyzer at room temperature in inert atmosphere with a three-electrode configuration in CH2Cl2 solution (purchased from Sigma-Aldrich) containing the substrate (typically 2 × 10 -3 M) and 0.1 M tetrabutylammonium hexafluorophosphate (n-Bu4NPF6) as the supporting electrolyte. A platinum disc, a platinum plate, and a silver wire electrode were served as the working electrode, the counter electrode and the quasi-reference electrode (QRE), respectively. All potentials were calibrated versus an aqueous SCE by the addition of ferrocene as an internal standard taking E1/2(Fc/Fc + ) = 0.424 V vs. SCE. [2] The scan rate was 0.1 V/s. The HOMO and LUMO energy values were estimated from the onset potentials of the first oxidation and reduction event, respectively. The HOMO and LUMO energy levels were calculated according to the following equations:

Association with Fullerenes
Single crystals of compound 1a-Me@C60 was grown by diffusing ethanol into its solution in odichlorobenzene, 1a-Me@C70 was grown by diffusing ethanol into its solution in toluene.

X-ray Crystallography for (1a-Me@C60)
Supplementary  (16) 92.016 (3) 97.445 (3) 109.711 (3) 3502.0(5)   (4) 33.234 (9) 27.770 (6)  Because the association constant could not be determined by NMR titration due the low solubility of complexes, we used fluorescence titration for quantitative analysis. To determine the association constant (Ka) of 1a-Me with C60 and C70, fluorescence spectral titration analysis was carried out in 1,2diclorobenzene. Stock solution A and B were prepared as shown in Supplementary Table 7. Titration was performed by successive addition of solution B into 2.0 mL of solution A. Excitation wavelength of 407 nm was used for emission spectra of 1a-Me. Due to the competition absorption of C60 and C70 at the excitation and emission wavelength of 1a-Me, the fluorescence intensity Fexp was calibrated to Fcal according to a well-established method. [10] where Fexp was the experimental fluorescence intensity; Fcal was the fluorescence intensity after calibration; 1c1l and 2c2l were the absorbance of the host 1a-Me and fullerene guest at excitation wavelength (ex=407nm), respectively, while 3c3l was the absorbance of fullerene guest at emission wavelength of host 1a-Me (em =514nm).
On the basis of the 1:1 complex model, association constant Ka is calculated by non-linear curve fitting (1stopt software with universal global optimation) using the following equation: where F0, Fcal, H0, G0, and Ka are fluorescence intensity of the 1a-Me before the addition of C60 or C70, fluorescence intensity after calibration, initial concentration of 1a-Me, initial concentration of C60 or C70, and the binding constant respectively. [11] Supplementary

DFT calculations
Quantum chemical computations were performed for 1a and 1b with all butyls replaced by hydrogen atoms (1a' and 1b'). This only has a marginal influence on the electronic properties of the systems, but significantly speeds up computational explorations. Geometric optimization was performed at B3LYP/6-311G(d,p) level of theory using the Gaussian 09, Revision D.01 program, [3] and some calculated results were processed by Multiwfn. [12] Electrostatic potential [13] calculations were conducted at B3LYP/6-311G(d,p) level. NICS(1)zz [14] were calculated using the gauge invariant atomic orbital (GIAO) approach at the GIAO-B3LYP/6-311G(d,p) level. Due to the bowl-shape structure, we used the average of NICS(1)zz (cocave) and NICS(-1)zz (convex) to evaluate the aromaticity character of each individual rings. AICD plot [15] was calculated by using the method developed by Herges at B3LYP/6-311G(d,p) level. TD-DFT calculations were conducted at PBE/def2tzvp level. Inversion barrier and dipole moment calculations were conducted at M062x/6-31G(d) level.

Binding energies of 1a-Me@C60 and 1a-Me@C70
All complexes evaluated were fully optimized at the B3LYP-D3/6-311G(d,p) level without symmetry constrain. The B3LYP-D3 functional was appropriate for large van der Waals interaction systems because the dispersion correction (D3) was an add-on to standard Kohn-Sham density functional theory (DFT), which has been refined for broader range of applicability, regarding higher accuracy and less empiricism. [16] The B3LYP-D3 functional has been demonstrated for a wide variety of noncovalent complexes. Binding energies Ebind for the association of C60 and C70 with 1a-Me were calculated by B3LYP-D3/6-311G(d,p) level. The counterpoise (CP) procedure was used to calculate the interaction energy in order to correct the basis set superposition error (BSSE) [17] and applied to only the optimized geometries of the complexes. Ebind can be expressed as the following equation:

Ebind = EHG(bHG) -[EH(bH) + EG(bG)] + EBSSE EBSSE = [EH(bH) -EH(bHG)] + [EG(bG) -EG(bHG)]
where subscript refers to the geometry (H for buckybowl, G for fullerene, HG for complex) and the parentheses indicates the basis set used. EH(bH) and EG(bG) are assumed to be monomer energies evaluated using each basis set for EH and EG. EHG(bHG) refers to complex energy evaluated using the full basis set of system HG. EBSSE refers to corrected energy for basis set superposition error.   ,p)).